Are Stockton Air Quality Monitoring Results a Cause for Concern?

Anonymous 5 years ago • updated by lee nguyen 1 month ago 1

An air monitoring station at Stockton measures PM10, PM2.5, NH3, NO2, NOx and has been operational for 8 months. There have been 20 failures of the PM10 50 ug/m3 criteria and 1 failure of PM2.5 25 ug/m3 advisory. Is this a cause for concern. 

Yes! It is. Particulate matter mass in the air consists of the directly emitted fraction, primary PM, and the

fraction formed in the atmosphere from precursor gases, secondary PM. The main precursor gases for
secondary inorganic PM are SO2, NOx and NH3. Volatile organic compounds (VOCs) contribute to the
organic secondary PM. The majority of long-range transported particulate mass is estimated to fall into
the PM2.5 size fraction50. http://couponpayoff.com/
The contribution of the above-mentioned pollutants to aerosol formation cannot be derived in a
straightforward manner from conventional emission estimates. They can be made more commensurate
with weight factors describing the fraction changing into aerosols and accounting for the molecular
weight differences. Aerosol formation factors (AF) have been suggested for Europe51 with respect to
their potential effects on health. The AF value is defined as the product of Ms/Mp, Y and F. Ms/Mp
denotes the ratio of the secondary aerosol molecule form to the gas emission component molecule. Y
describes the fraction of emission yielding to potential aerosol formation, and it is unity for all
components except for VOC. F denotes the fraction of emitted mass converted into secondary aerosols.
F was derived with an atmospheric model, which considered the whole Europe as one modeling domain
box, where advection and dispersion can be neglected and the atmospheric fate of the precursor depends
only on gas deposition and conversion into aerosol. It takes into account only the deposition of the
precursor gas (e.g. SO2), not the total deposition as this includes also the secondary aerosol (e.g. SO4)
contribution. The values are shown in Table 2.
The AF for primary PM is unity, since all emitted mass is transmitted to the atmosphere where it
may potentially have adverse health effects. Comprehensive emission inventories and time series of
PM10 for Europe were not available until recently, and were not considered51.
The values for F can vary depending on the atmospheric model application. Results from other
studies are cited51, which yielded F=0.50 for SO2 and NH3. Since no additional values for NO2 were
reported, an assumption of the same value for NO2 was made here for the variability assessment. The
values for the variability estimate are in parenthesis in Table 2.
The conversion yield of VOCs to secondary organic aerosols depends on its chemical structure and
meteorological conditions. The share of long carbon chain VOCs, which tend to have a relatively high
aerosol formation yield, is small in anthropogenic emissions. A rough estimate was made51 by assuming
that one quarter of VOCs have long carbon chains of more than six carbon atoms (Y=0.25), assigning
F=5% for aerosol yield and Ms/Mp=1.5 to account for additional oxygen atoms in secondary aerosol
form, leading to AF of 0.02. For PM10 this would lead to a minimal contribution of VOCs, which is in
contrast to observations with a significant organic component of 25-50%. The variability is explored by
assuming high values for these parameters: Y=0.5, F=0.20 and Ms/Mp=2, which lead to AF=0.20. 

Read more at: https://www3.epa.gov/ttnchie1/conference/ei12/part/johansson.pdf